It is convenient to handle a storage phosphor within cassettes that protect the storage phosphor from extraneous light and damage. This is particularly the case for storage phosphors in which the latent x-ray image stored in the storage phosphor is read by photo electrically detecting an emitted x-ray image formed by scanning the storage phosphor with stimulating radiation. An example of such a storage phosphor reader is disclosed in U.S. patent application Ser. No. 979,970, filed Nov. 23, 1992 commonly assigned, inventors Rogers and Dhurjaty. It is desirable to retain the storage phosphor within a cassette except during actual processing. Such a storage phosphor cassette is disclosed in U.S. patent application Ser. No. 800,799, filed Nov. 27, 1991, now U.S. Pat. No. 5,276,333 entitled "X-RAY CASSETTE HAVING REMOVABLE PHOTOGRAPHIC ELEMENT" by Jeffrey C. Robertson, which is incorporated herein by reference. A hooked extractor can be used with the storage phosphor cassette to move a storage phosphor plate to and from a storage phosphor reader for processing. It is desirable to provide an apparatus to automate the presentation of such cassettes to such an extractor so that a number of cassettes could be processed in succession without attention from an operator. It is also desirable that such an apparatus be able to accurately position cassettes sequentially to simplify removal and reinsertion of the storage phosphor plate and that the presentation apparatus be separate from the storage phosphor reader to permit interchange of units and reduce repair times.
In a storage phosphor reader/storage phosphor cassette autoloader system, it is desirable that the cassette be accurately positioned relative to the access opening of the storage phosphor reader so that damage to the cassette and consequently to the storage phosphor is avoided during loading and unloading. Accurate sensing of the position of the cassette is therefore essential. Concomitantly, the position sensor and sensor control should be reliable, maintenance free, inexpensive and relatively simple. Sensor systems which rely on micro switches or CCD arrays can be unreliable, expensive, complex and/or require too frequent maintenance.
There is thus a problem in a storage phosphor reader/storage phosphor cassette autoloader system in providing a cassette position sensor that is reliable, inexpensive, maintenance free and simple.